Bond strength is used in designing purpose of RCC

1. Bond and Development Length
The term bond in reinforced concrete (RC) refers to the interaction
between the reinforcing steel and the surrounding concrete
that allows for transfer of stress from the steel into the concrete or
vive versa.
it ensures strain compatibility to allow the composite action of
concrete and steel.
to ensure proper bond there should be no slip between the steel
and the surrounding concrete under service load.
Bond stress is longitudinal stress acting at interface of concrete and steel.

2. Mechanism of Force Transfer
Bond is a structural property that is dependent not only on the concrete
strength but also on the geometry of the reinforcing bar and the structural
member itself.
Bond force transfer mechanism for deformed reinforcing bars
Bearing forces on
deformations
Parallel and
perpendicular components of bearing

3. Longitudinal bearing and radial splitting stresses on concrete

4. Mechanism of Bond
Bond in RCC is achieved through the following mechanisms:
1. Chemical adhesion due to the products of hydration
2. Frictional resistance due to the surface roughness of the
reinforcement and the grip exerted by the concrete shrinkage
3. Mechanical interlock due to the ribs provided in the deformed
bars
Bond forces acting on steel and concrete

5. Types of Bond :
1. Local or Flexural Bond Stress
Unrestrained slip between steel and concrete

6. Bond forces acting on concrete and steel
Plane bar : bond is relatively weak owing to weak chemical adhesion and
mechanical friction between the concrete and steel , which is easily broken
at large loads as a result the bars are pulled through the concrete.
To prevent this, end anchorage in the form of hooks are often provided with
plane bars.
To avoid using hooks, deformed bars can be used. The projecting ribs of
deformed bars bear on the surrounding concrete and increase the bond
strength considerably.

7. Design bond stress bd : (IS 456-2000, Cl. 26.2.1 ,pg 43)
bd for plane bar in tension

8. 2.Anchorage or development length
Anchorage or development bond is the bond developed near the extreme ends
(or cut-off point) of a bar subjected to tension (or compression).(Cl.26.2.1,pg42)

9. Bends and Hooks : (IS 2502)
Anchorage in steel bars is normally provided in the form of bends and hooks.
Deformed steel bars are not provided with hooks only 900 bends are used.
The anchorage value of bend of bar is taken as 4 times the diameter of bar for every
450 bend .